Temperature modulated DSC (TMDSC) was tested concerning the possibility to separate the glass transition of the copolymer (BMA-co-MMA) component from the melting effect of the polyethylene (PE) in PE/BMA-co-MMA interpenetrating polymer networks prepared by in situ polymerisation. It was shown that a direct separation of both effects using TMDSC is not possible. The influence of the (excess) specific heat capacity of PE on the measured curve in the range of the glass transition of the copolymer is not negligible. With the TMDSC results of pure cross-linked PE (and because of the high accuracy of TMDSC) a procedure was found to estimate both the step height Delta(Cp)(T-g) and the temperature T-g of the glass transition of the copolymer phase. Additionally, an estimation of the degree of cross-linking of the PE phase is possible. The accuracy of standard DSC measurements is insufficient to apply successfully the procedure of data analysis developed for analysis of TMDSC results. In this case, the method of inflection point gives the chance to estimate the glass transition temperature of the copolymer phase.